Coagulation of blood is a complex process requiring the sequential interaction of a large number of components, nearly all of which are proteins. These components include fibrinogen and Factors II, V, VII, VIII, IX, X, XI, and XII. A lack of any of these components, or a nonfunctional component, can lead to an inability of the blood to clot when required, with resultant excessive and life-threatening blood loss to the patient.
Factor VIII (antihemophilic factor) is present at deficient levels, or is absent, in certain individuals. For example, persons who have a deficiency (or absence) of Factor VIII, i.e., persons suffering from hemophilia A, have blood which either fails to clot or clots only after longer periods of time than the time required for clotting in a person who has a normal level of Factor VIII.
Factor VIII is present in plasma as a high-molecular-weight complex (Factor VIII complex), which includes Factor VIII:C and von Willebrand factor (Factor VIII:R or vWf). Factor VIII:C promotes blood coagulation. Factor VIII:R promotes aggregation of platelets and, when incorporated into the Factor VIII complex, acts as a stabilizer for Factor VIII:C.
Purification of the Factor VIII complex has resulted in Factor VIII preparations which have a purity level of about 90% or greater, and which are sufficiently stable for storage for long periods of time in a lyophilized form. As used herein, purity means the amount of the specified protein as a percentage of the total amount of protein in a sample. However, highly-purified, lyophilized Factor VIII complex compositions, i.e., compositions with a high Factor VIII:C specific-activity, are difficult to reconstitute in aqueous solutions such as those required for use in intravenous injection. The purified solutions require contact with solvents for extended periods of time (about 5-6 min.) before they are resolubilized, and often result in reconstituted solutions which have poor clarity, thus wasting valuable time of hospital employees.
In addition, the reconstituted Factor VIII complex compositions have a limited life, requiring that the reconstituted compositions be discarded after a short period of time. This presents difficulties in the treatment of patients who require injections of Factor VIII complex to maintain blood-clotting ability. Typically, such patients are injected with a dose of about 50 units of Factor VIII:C/kg of body weight about every one to two weeks, although injection schedules vary from person to person depending on the severity of the individual's hemophilia.
In U.S. Pat. No. 4,650,858 to Rasmussen et al., Factor VIII is purified using a two-step PEG precipitation purification scheme, wherein an amino acid or other "salting-in" agent is added to the second PEG precipitation to salt-in contaminants and to give a "sharper" purification of the Factor VIII. The salting-in agent used in this method would be substantially removed from the final Factor VIII preparation as a result of the subsequent precipitation of the Factor VIII by PEG. The specific-activity of the Factor VIII is limited to only 3.85 to 50 units/mg.
There is a need to provide a lyophilized Factor VIII complex composition which has enhanced solubility in aqueous solutions. It is also desirable that the reconstituted Factor VIII complex is stable at room temperature, so that, once a solution is reconstituted, it can be stored for extended periods of time prior to use.